Project Summary/Abstract Drugs of abuse, such as heroin, have devastating effects on immune function and lead to addictive behavior. Remarkably, these effects of heroin are conditioned to environmental stimuli. The resulting conditioned immunomodulatory and motivational effects are robust, but the neural mechanisms of these effects are poorly understood. We have made major contributions to the understanding of the neural circuitry underlying conditioned immunomodulation and motivation. Building on these findings, this R01 proposal will test the overarching hypothesis that heroin-conditioned immunomodulation and motivation to seek drug rely on altered central nervous system signaling mediated by the cytokine, interleukin-1 (IL-1). Specific Aim I will test the hypothesis that exposure to heroin-conditioned stimuli is associated with IL-1 expression in distinct brain regions and cell types within the CNS. We will evaluate changes in IL-1 expression across time in the dorsal hippocampus (DH), basolateral amygdala (BLA), nucleus accumbens shell (NACs), and ventral tegmental area (VTA), after exposure to a heroin-conditioned context or after control manipulations designed to determine whether these alterations are due to conditioning per se. We will identify specific cell types involved in these effects. As follow-up, in the brain regions that exhibit conditioned IL-1 expression, we will explore whether IL-1 is sufficient to induce immunosuppression in the absence of heroin conditioning, by examining the effects of site- specific recombinant IL-1 infusion. Specific Aim II will test the hypothesis that IL-1 gene expression is necessary in specific brain regions for the expression of heroin-conditioned immunomodulation. To demonstrate that IL-1 expression is necessary for heroin-conditioned immunomodulation, we will examine the effects of inhibiting IL-1 expression in specific brain regions on heroin-conditioned immunomodulation. IL-1 gene expression in the DH, BLA, NACs, or VTA will be inhibited selectively using small interfering RNA (siRNA) or the IL-1 receptor will be blocked using IL-1 receptor antagonist in the same brain regions. Specific Aim III will be to test the hypothesis that IL-1 gene expression in the DH is necessary for the conditioned motivational effects of a heroin-paired context that facilitate drug seeking. We will test whether IL-1 expression is necessary for the motivational effects of drug-paired contextual stimuli using the conditioned place preference (CPP) paradigm, given its similarity to the heroin-conditioned immunosuppression procedure. We will also evaluate whether IL-1 expression is necessary for drug context-induced reinstatement of heroin-seeking behavior using the contextual reinstatement paradigm, a model of drug relapse with exceptional face and predictive validity. Overall, this project takes an innovative approach to reveal novel neuroimmunological mechanisms by which drug-conditioned stimuli impact immune function and drug relapse, thereby fundamentally enhancing our understanding of the health consequences of opioid use and informing the development of novel neuroimmunological therapies to restore immune function and prevent drug relapse.